In the current state of the art the weft gripper of a shuttleless loom is generally driven by a flexible polyester tape driven with reciprocating motion by a drive sprocket.
Such a flexible tape would however undergoes permanent deformation during operation with consequent loss of rectilinearity. It is essential to maintain rectilinearity to allow even slow transfer of the weft yarn between the grippers at the center of the shed. It has been found necessary to guide the tape along its entire travel by guide blocks which are positioned in staggered arrangement along the two sides of the tape and which comprise opposing C-shaped grooves in which the tape slides.
The guide blocks create a disturbance for the warp yarns. The warp yarns can undergo damage especially in the case of high density weaves. These guide blocks by their very pressure give rise to the danger of undesirable lines appearing on the forming fabric causing color nuances due to the rubbing of said blocks against the warp yarns. There is also the further drawback of tape wear by mechanical sliding between the grooves in the blocks.
In order to dispense with said guide blocks and hence obviate said drawbacks, it is necessary to replace the flexible polyester tapes with plastically indeformable tapes, i.e. laminated layer tapes containing rigid carbon, Kevlar, glass or other fibers. Such tapes cannot undergo permanent deformation and therefore do not lose their rectilinearity by repeated winding onto and unwinding from the respective drive sprocket.
A tape drive system for the weft gripper in a shuttleless loom which uses a rigid tape is already known.
This known system uses a non-toothed drive wheel about which the plastically indeformable tape is wound with its end fixed to the wheel periphery. This tape is made to perfectly adhere to the wheel periphery, against the effect of the arising centrifugal force, by an auxiliary pressing cable which passes about two idle pulleys and has its ends fixed to the wheel periphery.
Although this solution is effective, it is, however, evidently of very complicated structure and therefore costly. In addition, it has a certain inertia due to the masses in motion, thus limiting the maximum obtainable operating speed.
The object of the present invention is to obviate said drawbacks by providing a tape drive system for the weft gripper of a shuttleless loom which is extremely light and therefore of negligible inertia, and which, in addition, is simply constructed and thus of low cost.